The alignment and determination of an initial orientation is critical to the operation of any observation instrument, such as a telescope. Traditionally, a telescope is aligned by a two-star alignment process, where the telescope is aligned to a first star, and then the telescope is aligned to a second star. One of the requirements of the two-star alignment system is that the stars must be known.
There are numerous designs for mounting astronomical telescopes, including equatorial and altitude-azimuth (altazimuth or Alt-Az) mounts. A mount is said to be equatorial if one of its two axes can be made parallel with the Earth's axis of rotation. The equatorial mount includes a rotatable polar shaft (to be made parallel to the Earth's axis of rotation), a stationary support for the polar shaft, a rotatable declination shaft that is secured to the telescope, and a member which is secured to the polar shaft and which rotatably supports the declination shaft. In an equatorial mount configuration, aligning the telescope to the Earth's axis is needed for tracking objects across the sky (either manually or with a motor drive) at high magnifications. The alignment is also needed in order to use setting circles to locate faint or hard-to-find objects.
To achieve alignment, the polar shaft is initially positioned with its axis in the direction of the North Star, and the telescope is initially fixed on a target object (e.g., star, planet or moon), by rotating it on the shaft axes to a certain position. Because of the rotation of the earth, the polar shaft must be slowly rotated in order to hold the telescope fixed on the selected object. Both automatic and manual drive mechanisms have been provided for this purpose. The automatic devices usually include a motor that is secured to the stationary support and is connected to the polar shaft for rotating the polar shaft at sidereal rate.
Although the operation of the equatorial mount is simple in concept (i.e., only one axis has to be rotated to maintain tracking once the telescope is aligned), it has a number of drawbacks. For example, the drive mechanism for the equatorial mount can be a relatively complicated and expensive mechanism that cannot readily be installed by an average amateur astronomer. In addition, as the size of the telescope increases, a rather large diameter gear must be attached to the polar shaft to obtain the necessary torque to turn the polar shaft. Further, it is difficult to make small changes in the rate of rotation to maintain a fix on a planet or the moon with drive mechanisms that do not have variable drive rates.
An Alt-Az mount is a mount in which, with respect to the surface of the Earth, one axis (altitude) is vertical and the other (azimuth) is horizontal. Although both axes must be driven at rates that vary with the position in order to maintain tracking to the target object, a computer can easily handle the variable drive rates. The benefits of the Alt-Az mounting become more important as the telescope becomes larger. For example, rotation about the vertical altitude axis does not change the orientation of the telescope tube with respect to gravity, so that this motion does not change any aspect of the flexure of the support. In effect, an Alt-Az mount is a fork mounting with one of the axes vertical so that the tines have no transverse load at all. The Alt-Az mount obviates the twisting of the fork tines that makes it so difficult to design the declination axle bearings of the equatorially mounted telescope. Longer tines are now practicable and the horizontal elevation (altitude) axis can be nearer the mid-point of the telescope tube.
Regardless of which type of mount is used, it must be aligned in order for any telescope to be setup. For example, for a computerized telescope to be aligned to the sky, it needs at least two alignment stars as reference. For experienced telescope users and astronomers, this is not a problem because they can identify many of the stars in the sky. However, for a beginner, the alignment process can be a big obstacle. A beginner may not be able to locate or identify any of the stars to be able to align the telescope. Thus, a beginner cannot point the telescope to a star and tell the telescope that it is pointed at a particular star. Further, even in conventional alignment systems such as that described by U.S. Pat. No. 6,392,799, entitled “Fully Automated Telescope System with Distributed Intelligence,” where the mount may be aligned by being positioned with respect to terrestrial orientations (such as being leveled and pointed in a particular magnetic direction), the user has to know a particular magnetic direction (e.g., North), and level the mount with respect to the horizontal.
A “fully” automated alignment system has been proposed in “Automatic Telescope”, filed as U.S. patent application Ser. No. 10/438,127 on May 14, 2003, and published as U.S. Patent Application Pub. No. US2004/0233521, describes an alignment system that does not require the user to interact with the telescope during the alignment process. Specifically, this system describes the use of angular separations between a group of “bright” stars that is chosen by an imager in the telescope as data points to help identify the stars.
As angular separation between stars does not change with the observer's time or location (and hence the time/location does not need to be known), this system has the advantage of not needing an accurate time or location input and also has the advantage of being able to derive the local sidereal time (a relative measurement of time based on the observer's location) once the identification is complete. However, this system anticipates the need to use four stars to generate six unique data points that can then be used to reliably identify the stars from an exemplary field of stars in FIG. 1, as illustrated in FIG. 2. In addition, this system is less accessible to beginning users with small telescopes because the system includes the added cost of an imaging system along with the cost for a processor that can support the processing needed for the images generated by the imaging system as well as the alignment procedure of the align system itself.
Further, certain environments can make locating bright stars difficult with a fully automated system. For example, transient objects like airplanes can confuse the system as the warning strobes on the planes may fool it into identifying the plane as a “bright object.” Also, automated systems do not have awareness of—and therefore will not avoid scanning of—obstructed portions of the sky (e.g., portions of the sky blocked by trees, clouds, building, etc.). A particularly problematic situation would be where a user wishes to perform an automated alignment from a location such as the balcony of a high-rise building.
One benefit often touted for automated alignment systems is that they are supposed to make set-up enjoyable and simple for the novice user. Ironically, a fully automated approach reduces the educational aspect of setting up a telescope because, during the setup process performed by these automated systems, it is often not obvious where the telescope is pointing to acquire alignment objects and hence the user would not gain any insight into the night sky. Even if the automated system included an imager, and a display is attached to it so as to display the images captured from the imager, the user still will not gain any sense for where the telescope is actually pointing. For example, if the user is standing at a telescope that is pointing somewhere, it will be difficult for the user to tell which one of the stars in the sky at which the telescope is actually pointing—even if the display is displaying the star and the star's name. Thus, the user would have to go to the telescope and sight along the tube or look through a finderscope.
Accordingly, there is a need to overcome the issues noted above.